Patients with systemic lupus (SLE) often excessive type I interferon production, with activation of interferon-inducible genes (interferon signature). The mitochondrial adaptor protein MAVS (IPS1, VISA or CARDIF) is a key intermediary in the RIG-I pathway, where viral RNA triggers a conformational change in RIG-I, leading to MAVS activation and activation of IKK and TBK1, with subsequent interferon production driven by IRF-3 and NFkB activation and translocation. A recent report using in vitro methods demonstrated that MAVS may form large prion-like aggregates which might stimulate IFN-I activation in a potent and prolonged fashion. Remarkably, we have found that cells from ~40% of SLE patients showed clear MAVS aggregation, with essentially all of their MAVS protein in a high molecular weight form. Such MAVS aggregation is not seen in cells from normal individuals. In this proposal, we will extend and confirm our observations, and will correlate aggregate-positive samples with clinical disease patterns and disease activity. We will examine interferon type I production of cells isolated from patients with MAVS aggregation for enhanced production of IFN, and will perform array analysis to measure their interferon signature. We will determine the source of aggregated MAVS by analysis of separated cell populations from the blood of SLE patients. We will ask if the MAVS-inhibitory protein NLRX1 is under-expressed in lupus patient cells. Finally, we will determine the significance of MAVS on IFN-I production by measuring IFN production after blocking MAVS activation through intervening in several signaling pathways involving MAVS. These studies address a fundamental question in lupus pathogenesis and should give insight into the innate immune response driving the disease.